The assignee of the present invention designs and manufactures spacecraft for communications and broadcast services. Electrical power for such spacecraft is conventionally generated by photovoltaic solar arrays, typically having several thousands of solar cells.
Solar cells of numerous varieties are known, but typical features of the types of cells with which the present inventors are concerned, are illustrated in FIG. 1. Referring to cross-sectional schematic view FIG. 1A, and top view FIG. 1B, solar cell 100 has a semiconductor substrate 110 having a base region or layer 112 formed of a first conductivity type below an emitter region or layer 114 of opposite conductivity type. A metallized conductor on the back surface of the base region forms electrode 120. A grid on the front surface of the emitter region, which surface is the light receiving surface, forms a second electrode. The grid, typically composed of fine metallic lines 130, is conductively coupled to at least one current collector bar 140, and may be covered by a cover glass (not shown). For improved packing densities, cells having a substantially rectilinear (square or rectangular) footprint are preferable. Referring to FIG. 1C, a substantially rectilinear cell may have one or more relatively short corner edge segments 150 disposed at an obtuse angle to the main side edges 160.
Referring now to FIG. 2A, in order to connect an electrical series (or “string” 201) of solar cells, one or more cell interconnects 270 may be disposed between adjacent cells that conductively couple back surface electrode 120 of one cell to current collector bar 140 of the next cell in string 201.
Solar arrays that may advantageously employ the present invention are described, for example, in Hoeber, et al., U.S. Pat. No. 6,248,950, (hereinafter, “Hoeber”), and assigned to the present assignee, the content of which is hereby incorporated into the present application in its entirety. As disclosed in Hoeber, a known solar array scheme provides for a number of strings to be connected in parallel. As Hoeber also discloses, it has been found advantageous to arrange each individual string in a spiral arrangement, because doing so reduces the maximum voltage difference between any two adjacent cells. An example of a spiral arrangement of solar cells of the aforementioned type is illustrated in FIG. 2B. In the illustrated example, a string 200 of solar cells 100 extends from and between (positive) busbar terminal 280 at cell 100(8) and (return) busbar terminal 280 at cell 100(1). Vertically aligned, adjacent, cells are electrically connected by interconnects 270. Other cells, for example, cell 100(2) and cell 100(3), cell 100(4) and cell 100(5), and cell 100(6) and cell 100(7), are connected by electrical wiring 290, attached to respective busbar terminals 280.
As the demand for higher power spacecraft has grown, so has the demand for higher power solar arrays, each array typically consisting of two or more solar panels, with a consequent requirement to arrange even higher numbers of solar cells on each solar panel. This in turn places an increased emphasis on improving the ratio of solar cell area to solar panel area (hereinafter, “the panel packing ratio”) and in achieving increased reliability and cost efficiencies in making the necessary electrical connections between cells.
In light of the foregoing, solar cell configurations, whether for space or for ground applications, that permit improvements in the above mentioned metrics, are desirable.